The Messenger of Allah ﷺ said, "Fasting is a shield. When one of you is fasting on a given day, he should not engage in obscene speech or behave ignorantly. If someone tries to fight him or insult him, let him say, 'I am fasting, I am fasting.'"
حدثنا يزيد أخبرنا محمد عن موسى بن يسار عن أبي هريرة وعن أبي الزناد عن الأعرج
قال رسول الله ﷺ الصيام جنة وإذا كان أحدكم يوما صائما فلا يرفث ولا يجهل وإن امرؤ قاتله أو شاتمه فليقل إني صائم إني صائم
It has two sahih chains of transmission. Muhammad bin Ishaq narrated it from Musa bin Yasar from Abu Hurairah, and he also narrated it from Abu Zinad from Araj from Abu Hurairah. Ibn Ishaq narrates from Araj directly, but he narrated this hadith, and the hadiths after it, 7486–7493, from Abu Zinad from Araj.These narrations refute those who accused him of extensive concealment of his sources, on account of which his narration is set aside unless he explicitly states that he heard it directly.The meaning of this hadith has already appeared in abridged form at 7336, through the narration of Sufyan from Abu Zinad. His statement here at the beginning, "Fasting is a shield," was also narrated by Bukhari, 4:87-88, through the route of Malik from Abu Zinad. Muslim narrated it alone, without the rest of the hadith, 1:316, through the narration of Mughira Hizami from Abu Zinad.